The invention generally relates to systems that compensate for the weight of the load borne by a railcar in formulating the braking effort to be applied to the wheels of the railcar. More particularly, the invention pertains to a simplified pneumatic system that can be used as a backup to an electronic system that normally provides load compensation on a railcar during both service and emergency applications of the brakes.
The following background information introduces one of the many possible environments in which the invention can be used. This information is provided to assist the reader to understand the invention, as novel material is often more readily understood if described in a familiar context. The terms used herein are not intended to be limited to any particular narrow interpretation unless expressly stated otherwise in this document.
A passenger transit train typically includes a locomotive, a plurality of railcars and several trainlines. The brake control system in such a train typically features a central controller in the locomotive through which to control the brakes on the trucks of all the vehicles that comprise the train. Riding in the locomotive, a train operator uses a brake handle or like device to apply and release the brakes as desired. The inputs from the brake handle(s) are typically processed by a cab control unit and passed to the central controller. In response to these and other inputs, the central controller then sends a brake command signal to the vehicles of the train in the form of either a pneumatic signal or an electrical signal or even both.
The trainlines include both pneumatic and electrical lines, most of which run from the locomotive to the last railcar in the train. The main reservoir (MR) pipe is one such pneumatic trainline. It consists of a series of individual pipe lengths. Secured to the underside of each railcar, one such pipe length connects via a coupler to another such pipe length secured to a neighboring railcar. Essentially one long continuous pipe that runs the length of the train, the MR pipe is charged by various air compressors dispersed throughout the train. The brake control system uses the MR pipe to supply air to the various known reservoirs and to supply the air that is needed to charge the brake cylinders of each truck during brake applications.
In the passenger transit industry, many trains are equipped with a type of brake control system that directs control of the brakes via a pneumatic trainline known as the brake pipe. In such brake control systems, the brake pipe is the conduit through which the brake commands are carried to all the vehicles in the train.
An example of such a brake pipe controlled system is the PT-2000 Brake Control System produced by the Westinghouse Air Brake Technologies Corporation (WABTEC). Based on the 26-C Style approach, the PT-2000 Brake Control System employs, in addition to the brake pipe, an electrical trainline along which brake command signals are conveyed to the brake equipment on the trucks of each railcar. Akin to the brake pipe, the conduit in which the electrical trainline is housed actually constitutes a series of individual conduits. One such conduit secured to the underside of each railcar interconnects to another such conduit via a connector between each vehicle. The brake equipment on each truck applies or releases the brakes according to the dictates of the particular brake command signal received from the central controller.
Each railcar typically includes two trucks, with each truck having its own electronic control unit. The electronic control unit receives the brake command signal sent by the central controller in the locomotive. It does so directly via the electrical trainline and/or indirectly via the brake pipe with the aid of one or more pressure transducers. In response to the brake command signal and to various other inputs specific to its own truck, the electronic control unit controls the electropneumatic brake equipment of its truck independently of the other truck.
On a passenger train equipped with a PT-2000 Brake Control System, the electronic control unit takes the form of a Communication Based Electronic Control Unit (CBECU), which is part of a communications network on the train. The electropneumatic brake equipment onboard each truck includes a truck control valve (TCV), the construction and operation of which are well known in the brake control art. The CBECU on each truck receives the brake command signal and various other signals in response to which it directly controls the TCV on the truck according to principles well known in the brake control art.
The TCV has an electropneumatic portion and a relay valve portion. The relay valve portion features a control port to which the flow of air from a source of pressure, such as the MR pipe, is controlled by the electropneumatic portion. The relay valve portion also features a supply port that connects to a source of pressurized air, an output port from which air at the supply port can be directed to the brake cylinder of the truck, and an exhaust port from which to vent the brake cylinder to atmosphere. From its output port, the relay valve portion delivers to the brake cylinder air whose pressure is proportional to the pressure impinging on its control port, though in a much greater capacity. When pressurized, the brake cylinder converts the pressurized air that it receives to mechanical force. This mechanical force is transmitted by mechanical linkage to the brake shoes. Forced against the wheels and/or disc brakes, the brake shoes are used to slow or stop the rotation of the wheels. The magnitude of the braking force applied to the wheels is directly proportional to the pressure built up in the brake cylinder.
During normal operation, the CBECU controls the electropneumatic portion of the TCV. Using the brake command and various other known inputs, the CBECU formulates the final signals with which it controls known valves within the electropneumatic portion. Using such signals according to known algorithms, the CBECU enables the electropneumatic portion to control whether, and how much, air from the MR pipe will reach the control port of the relay valve portion. The CBECU therefore enables the electropneumatic portion to control how much air will be delivered to the brake cylinder and thus the extent to which the brakes on the truck will apply. In doing so, it can not only perform various desired functions such as wheel slip control but also electronically compensate for the load borne by the truck during both service and emergency brake applications.
Whenever there is a loss of power or other electrical failure, however, the CBECU loses its ability to control the electropneumatic portion of the TCV. This causes the TCV to connect the control port of its relay valve portion directly to the source of pressure (e.g., the MR pipe) during a brake application. Because a TCV acts merely as a relay valve whenever its power is lost, the TCV will provide to the brake cylinder the same pressure it receives at its control port, but in a higher capacity. Consequently, whenever a power failure occurs, the TCV loses its ability to compensate for the load borne by the truck during both service and emergency brake applications.
For passenger transit trains, it is particularly desirable to compensate for load in determining the force with which the brakes should apply. On transit trains whose railcars employ load compensation techniques, the problems typically associated with wide variances in weight, such as elevated buff (compressive) and draft (tensive) forces among railcars, are reduced considerably.
Brake pipe controlled brake control systems have traditionally required a considerable amount of devices to perform load compensation. In 26-C Style passenger trains, the following devices were required at the very least: 26-C Style brake control valves, multiple diaphragm relay valves, small capacity transfer valves, double check valves, bypass limiting valves, and standard variable load valves. Some of these devices impose certain operational disadvantages. Multiple diaphragm relay valves, for example, tend to fix pressure ratios (i.e., pressure at full service versus that during an emergency) to a very limited number of combinations. These devices are also quite heavy, occupy a considerable amount of space, and taken together, constitute a rather complex way of performing load compensation.
It would therefore be desirable to devise a simplified system of providing load compensation for the railcars of a brake pipe controlled passenger train, especially one capable of doing so whenever a loss of power or other electrical failure occurs. It would be particularly desirable if such a system could provide load compensation during both service and emergency brake applications. Such a simplified system would ideally be installed on railcars of the type equipped with PT-2000 brake equipment. Current railcars, particularly those equipped with 26-C Style brake equipment, lack such a simplified system of compensating for load.
It is, therefore, an objective of the invention to provide a load compensation system that will compensate for the load a railcar bears during both service and emergency brake applications whenever a loss of power or other electrical failure occurs.
Another objective is to provide a load compensation system that is simpler in design, lighter in weight, fewer in parts, and smaller in size than prior art load compensation schemes.
A further objective is to provide a load compensation system that employs a four-port variable load valve on a railcar equipped with simplified brake pipe control valve technology.
Yet another objective is to provide a simplified load compensation system that serves as a pneumatic backup, whenever a power failure occurs, to the electronic load compensation system on a railcar equipped with brake pipe controlled brake equipment.
In addition to the objectives and advantages listed above, various other objectives and advantages of the invention will become more readily apparent to persons skilled in the relevant art from a reading of the detailed description section of this document. The other objectives and advantages will become particularly apparent when the detailed description is considered along with the drawings and claims presented herein.
The foregoing objectives and advantages are attained by a simplified pneumatic backup system. It is designed to backup pneumatically an electronic system that normally provides load compensation on a railcar truck during both service and emergency applications of the brakes. The truck is of the type equipped with brake pipe controlled brake equipment including an MR pipe, a brake pipe, and a TCV. In its most basic form, the backup system comprises a variable load valve, a main relay valve, a main control valve, and a main transfer valve. The variable load valve has supply and control ports, both in communication with a distribution network. It also has a load weigh port for receiving pressure indicative of load borne by the railcar and an emergency port for receiving pressure via an emergency network. From its output port, the variable load valve provides (I) a first load compensated pressure in response to pressure at its control and load weigh ports and (II) a second load compensated pressure in response to pressure at its control, load weigh and emergency ports. The main relay valve has a supply port linked to the MR pipe and a control port connected to the output port of the variable load valve. From its output port, the main relay valve provides an output pressure proportional to the pressure acting on its control port. The main control valve includes an emergency valve and a 3-way valve. The emergency valve vents the emergency network as long as the brake pipe pressure stays above an emergency level, below which the emergency valve links the distribution and emergency networks. The 3-way valve includes a first pilot port in communication with the brake pipe and a second pilot port communicating with a control reservoir. The main transfer valve operates in a piloted state or an unpiloted state. In the piloted state, the transfer valve disconnects the TCV from the output port of the main relay valve and links the TCV to the MR pipe thereby placing the main control valve in a cut-out mode. In the unpiloted state, the transfer valve links the TCV to the output port of the main relay valve thereby placing the main control valve in a cut-in mode wherein the 3-way valve responds by assuming one of three states. In response to the brake pipe pressure increasing relative to the pressure in the control reservoir, the 3-way valve assumes the release state wherein it exhausts the supply and control ports of the variable load valve and thus prevents the main relay valve from outputting an output pressure. In response to the brake pipe pressure dropping relative to the pressure in the control reservoir yet remaining above the emergency level, the 3-way valve assumes the service state. In this state, the 3-way valve links the MR pipe with the distribution network thereby allowing pressure to build against the supply and control ports of the variable load valve. The variable load valve responds by outputting the first load compensated pressure. This causes the main relay valve to output to the TCV an output pressure proportional to the first load compensated pressure. In the emergency state, the 3-way valve continues operating according to the service state yet the brake pipe pressure falls below the emergency level. This causes the emergency valve to link the emergency network with the distribution network thereby allowing pressure from the MR pipe to build against the emergency port. The variable load valve responds by outputting the second load compensated pressure. This causes the main relay valve to output to the TCV an output pressure proportional to the second load compensated pressure.